Watch: Underwear Mistakes You're Probably Making

Here are some common underwear mistakes you might be making.

1. Not wearing cotton. Silk and synthetic fabrics don't breathe like cotton does, which can create a breeding ground for bacteria.

2. Wearing the wrong size. Underwear that's too big looks saggy and messy. But too-tight underwear is even WORSE because it can cause chafing and irritation.

3. Wearing them to bed. It keeps that area from getting air, and there's the possibility of trapped moisture causing problems.

4. Putting them in the dryer. The heat in a dryer breaks down fabrics, so the elastic in your waistband will stretch out over time. It's better to air dry them.

5. Not buying new ones. A recent study found that you should be throwing out your underwear and buying new ones about every YEAR. It's because bacteria like E. coli can build-up even if you wash them regularly, and can cause some nasty infections.